High-occupancy vehicle restrictions and the return of mass transit created a fresh nightmare for the flood of commuters trying to cram into Manhattan yesterday — backing up traffic for miles and causing long lines squeezing to get on shuttle buses.

Police checkpoints were set up to enforce the rule of three people per vehicle and avoid a repeat of Wednesday’s staggering gridlock, but it also led to hour-long waits to cross the East and Hudson rivers.

And clueless cops mistakenly set up a checkpoint on the exempt George Washington Bridge, causing unnecessary jams until Gov. Cuomo called off the NYPD.

Drivers desperate to cross East River bridges picked up complete strangers, who were ecstatic to escape the mass-transit hell in Downtown Brooklyn.

The same HOV restrictions will be enforced again today. But Mayor Bloomberg said he hopes it will be the last day of these strict driving rules.

Thousands of people lined up for six blocks outside the new Barclays Center and Jay Street-MetroTech to catch shuttle buses to Manhattan.

“It’s very hostile waiting in that line. It was overwhelming,” said Ray Qi, who tried to hitch a ride into the city but ended up going home. “I felt like I was in the movie ‘Avatar,’ where everyone is waiting to be deported. It’s scary!”

The large-scale return to work was among several Hurricane Sandy developments yesterday:

* The already grim death toll from the Frankenstorm rose to 40, including two adorable young brothers who were swept away in a torrent of water on Staten Island.

* Power remained out for nearly 230,000 lower Manhattan customers, who could get their juice back by tomorrow. A total of 534,000 customers citywide remained without power, and it could take nine more days to restore outer-borough service.

Another 1.7 million customers remained without power in New Jersey, and officials said it could take 10 more days to restore electricity completely. Lines at gas stations stretched for two miles in the state.

* More than half of city gas stations were unable to sell fuel, either because they had run out or were without power. “We really don’t know when [sales will resume] because the distributors aren’t telling us,” said Raman Kumar, manager of a Gulf station in Bayside, Queens.

* Gov. Cuomo activated the National Guard to deliver a million meals and bottled water to city residents stranded without power. At one distribution point at South and Catherine streets on the Lower East Side, supplies ran out and residents were told to come back today. But officials did open fire hydrants for residents to fill up water jugs and buckets.

* The damage estimate rose to $30 billion to $50 billion — with just $10 billion to $20 billion of that insured.

Cuomo asked Napolitano for a 100-percent reimbursement of the state’s hurricane-related costs — but Napolitano didn’t make any commitments on funding.

* Napolitano said the Federal Emergency Management Agency was doing everything possible to help the state, including sending 60 crews and equipment on a C-130 cargo plane to help in power restoration.

The White House said 17 military transport planes would be airlifting utility repair crews to the region — and it also dispatched three warships closer to the area.

* Another big storm, a nor’easter, could slam into the Sandy-ravaged city by next Wednesday, according to one forecast.

* Staten Islanders fumed about a lackluster response to their hard-hit borough, which suffered 20 confirmed deaths and major damage to thousands of homes by a “tsunami”-like storm surge.

Hundreds of homes still can’t be accessed, people are missing and cars and boats that were tossed around like beach balls are resting on fences or blocking streets.

* Residents of Broad Channel, Queens, told Schumer and other officials that they were worried about their houses’ oil tanks, many of which had floated away or were leaking. They also said they had to chase away thugs prowling around in the dark.

* Crime continued its comeback as 18 looters were busted breaking into a Coney Island grocery store, and thieves were reported to be snatching iPhones from people using them as flashlights in blacked-out lower Manhattan.

* Search-and-rescue teams from as far away as Virginia joined the FDNY to knock on doors of 19,000 homes looking for victims and survivors in the areas hardest hit by Sandy, sources said.

“If we come upon a door that’s open and no one answers, we’re going inside and looking around,” a source said.

* Bloomberg announced that the Board of Elections would find alternate locations for polling stations that would normally be in schools if those schools remain without power on Tuesday, Election Day.

* The Post’s parent company, News Corp., donated $1 million for Sandy relief and NBCUniversal is putting on a benefit concert for the Red Cross with performers including Bruce Springsteen, Jon Bon Jovi and Billy Joel.

* The environmental group Greenpeace sent a solar-panel-fitted truck, Rolling Sunlight, to the Rockaways yesterday to provide cellphone charging to residents.

* More than 4,000 couples had wedding plans interrupted by Sandy, according to TheKnot.com.